Lost Intimacy with my wife

So my wife is arguably above average in attractiveness and we have been married for abt 3 years, i see Men lusting over her, i see them checking her out whenever we go out and its been a while since i have had this fantasy of her being with other Men and i have lost the intimacy and the desire to be sexual with her for months now and i know she has noticed that change too, i get hard now thinking abt her being intimate with other men watching them drool over her makes me hard...i wanna talk to her abt this... but i dont know how i can bring this up...